Lead Integrity Testing During Suspected Tachyarrhythmias

1. A method comprising: detecting a suspected tachyarrhythmia via at least one implantable medical lead; in response to detecting the suspected tachyarrhythmia, measuring an impedance of the lead a plurality of times during the suspected tachyarrhythmia to obtain a plurality of impedance measurements; comparing the impedance measurements; and evaluating integrity of the lead based upon the comparison, wherein the suspected tachyarrhythmia comprises a plurality of sensed events, and wherein measuring an impedance of the lead a plurality of times during the suspected tachyarrhythmia comprises measuring the impedance at least two times between a consecutive two of the plurality of sensed events.

2. The method of claim 1 , wherein measuring an impedance of the lead a plurality of times during the suspected tachyarrhythmia comprises measuring the impedance at least three times between a consecutive two of the plurality of sensed events.

3. The method of claim 1 , wherein measuring an impedance of the lead a plurality of times during the suspected tachyarrhythmia comprises: delivering a plurality of test pulses via the lead, wherein delivering the plurality of test pulses comprises controlling a timing of the pulses to avoid interference with electrical sensing of cardiac events; and measuring a respective one of the plurality of impedance measurements based on delivery of each of the plurality of test pulses.

4. The method of claim 3 , wherein controlling the timing of the pulses comprises delivering the pulses during a period subsequent to one of the sensed events, and wherein a duration of the period is predetermined based on a previously measured tachyarrhythmia rate of a patient in which the lead is implanted or at least one other patient.

5. The method of claim 1 , wherein comparing the impedance measurements comprises determining a variability of the impedance measurements, and wherein evaluating lead integrity comprises evaluating lead integrity based on the variability.

6. The method of claim 5 , wherein the plurality of impedance measurements comprises a plurality of suspected tachyarrhythmia impedance measurements, the method further comprising: measuring the impedance of the lead a plurality of times prior to the detection of the suspected tachyarrhythmia to obtain a plurality of non-tachyarrhythmia impedance measurements; determining a variability of the non-tachyarrhythmia impedance measurements; and determining a tachyarrhythmia impedance measurement variability threshold based on the variability of the non-tachyarrhythmia impedance measurements, and wherein evaluating lead integrity based on the variability comprises comparing the variability of the suspected tachyarrhythmia impedance measurements the tachyarrhythmia impedance measurement variability threshold.

7. The method of claim 1 , wherein the plurality of impedance measurements comprises a plurality of suspected tachyarrhythmia impedance measurements, the method further comprising: measuring the impedance of the lead at least once prior to the detection of the suspected tachyarrhythmia to obtain at least one non-tachyarrhythmia impedance measurement; and comparing the suspected tachyarrhythmia impedance measurements to the non-tachyarrhythmia impedance measurement, and wherein evaluating the integrity of the lead further comprises evaluating the integrity of the lead based on the comparison of the suspected tachyarrhythmia impedance measurements to the non-tachyarrhythmia impedance measurement.

8. The method of claim 1 , further comprising switching to an alternative electrode combination for at least one of sensing of cardiac events or delivery of stimulation based on the evaluation.

9. The method of claim 1 , further comprising providing an alert to a user based on the evaluation.

10. The method of claim 1 , further comprising withholding delivery of a responsive therapeutic shock for the suspected tachyarrhythmia based on the evaluation.

11. A system comprising: an implantable medical lead; an implantable medical device (IMD) coupled to the lead, wherein the IMD detects a suspected tachyarrhythmia via the lead and, in response to detecting the suspected tachyarrhythmia, measures an impedance of the lead a plurality of times during the suspected tachyarrhythmia; and a processor that compares the measured impedances, and evaluates integrity of the lead based upon the comparison, wherein the suspected tachyarrhythmia comprises a plurality of sensed events, and wherein the IMD measures the impedance at least two times between a consecutive two of the plurality of sensed events.

12. The system of claim 11 , wherein the IMD measures the impedance at least three times between a consecutive two of the plurality of sensed events.

13. The system of claim 11 , wherein the IMD delivers a plurality of test pulses via the lead, controls a timing of the pulses to avoid interference with electrical sensing of cardiac events, and measures a respective one of the plurality of impedance measurements based on delivery of each of the plurality of test pulses.

14. The system of claim 13 , wherein the IMD delivers the pulses during a period subsequent to one of the sensed events, and wherein a duration of the period is predetermined based on a previously measured tachyarrhythmia rate of a patient in which the lead is implanted or at least one other patient.

15. The system of claim 11 , wherein the processor determines a variability of the impedance measurements, and evaluates lead integrity based on the variability.

16. The system of claim 15 , wherein the plurality of impedance measurements comprises a plurality of suspected tachyarrhythmia impedance measurements, wherein the IMD measures the impedance of the lead a plurality of times prior to the detection of the suspected tachyarrhythmia to obtain a plurality of non-tachyarrhythmia impedance measurements, and wherein the processor determines a variability of the non-tachyarrhythmia impedance measurements, determines a tachyarrhythmia impedance measurement variability threshold based on the variability of the non-tachyarrhythmia impedance measurements, and compares the variability of the suspected tachyarrhythmia impedance measurements the tachyarrhythmia impedance measurement variability threshold to evaluate the integrity of the lead.

17. The system of claim 11 , wherein the plurality of impedance measurements comprises a plurality of suspected tachyarrhythmia impedance measurements, wherein the IMD measures the impedance of the lead at least once prior to the detection of the suspected tachyarrhythmia to obtain at least one non-tachyarrhythmia impedance measurement, and wherein the processor compares the suspected tachyarrhythmia impedance measurements to the non-tachyarrhythmia impedance measurement, and evaluates the integrity of the lead based on the comparison of the suspected tachyarrhythmia impedance measurements to the non-tachyarrhythmia impedance measurement.

18. The system of claim 11 , wherein the processor controls the IMD to switch to an alternative electrode combination for at least one of sensing of cardiac events or delivery of stimulation based on the evaluation.

19. The system of claim 11 , wherein the processor provides an alert to a user based on the evaluation.

20. The system of claim 11 , wherein the processor controls the IMD to withhold delivery of a responsive therapeutic shock for the suspected tachyarrhythmia based on the evaluation.

21. The system of claim 11 , wherein the processor comprises a processor of the IMD.

22. A computer-readable medium comprising instructions that cause a processor to: detect a suspected tachyarrhythmia via at least one implantable medical lead; in response to detecting the suspected tachyarrhythmia, control measurement of an impedance of the lead a plurality of times during the suspected tachyarrhythmia to obtain a plurality of impedance measurements; compare the impedance measurements; and evaluate integrity of the lead based upon the comparison, wherein the suspected tachyarrhythmia comprises a plurality of sensed events, and wherein the instructions that cause the processor to control measurement of an impedance of the lead a plurality of times during the suspected tachyarrhythmia comprise instructions that cause a processor to control measurement of the impedance at least two times between a consecutive two of the plurality of sensed events.

23. The computer-readable medium of claim 22 , wherein the instructions that cause the processor to control measurement of an impedance of the lead a plurality of times during the suspected tachyarrhythmia comprise instructions that cause a processor to control measurement of the impedance at least three times between a consecutive two of the plurality of sensed events.

24. A system comprising: means for detecting a suspected tachyarrhythmia via at least one implantable medical lead; means for measuring an impedance of the lead a plurality of times during the suspected tachyarrhythmia to obtain a plurality of impedance measurements in response to detecting the suspected tachyarrhythmia; means for comparing the impedance measurements; and means for evaluating integrity of the lead based upon the comparison, wherein the suspected tachyarrhythmia comprises a plurality of sensed events, and wherein the means for measuring an impedance of the lead a plurality of times during the suspected tachyarrhythmia comprises means for measuring the impedance at least two times between a consecutive two of the plurality of sensed events.

25. The system of claim 24 , wherein the means for measuring an impedance of the lead a plurality of times during the suspected tachyarrhythmia comprises means for measuring the impedance at least three times between a consecutive two of the plurality of sensed events.